Sound reproducing apparatus

ABSTRACT

Sound reproducing apparatus, for example a loudspeaker unit in a hi-fi system, having a cabinet mounting on its front face a bass speaker unit and having two treble units, one being mounted on each of the front and rear faces of the cabinet.

United States Patent [191 Latimer-Sayer 1 1 SOUND REPRODUCING APPARATUS [76] Inventor: Laurence Latimer-Sayer,

Greenways, 122, Strawberry Vale, Twickenham, Middlesex TW1 4SH,

England {22] Filed: Nov. 6, 1973 [21] Appl. No.: 413,290

[30] Foreign Application Priority Data Nov. 10, 1972 United Kingdom 51918/72 Dec. 11, 1972 United Kingdom 57030/72 Jan. 19,1973 United Kingdom 2804/72 [52] U.S. C1. 181/144; 181/154; 181/156 [51] Int. Cl. H05K 5/00 [58] Field of Search18l/31 B, 31 A, 31 R, 144-148, 181/154,156,199; 179/1 E [56] References Cited UNITED STATES PATENTS 2,160,283 5/1939 Roberts 181/154 1 Dec. 2, 1975 2,550,336 4/1951 Daniel 181/154 2,722,990 11/1955 West 181/154 2,866,513 12/1958 White..... 181/156 3,393,764 7/1968 Schafer... 181/146 3,590,942 7/1971 Globa 181/146 OTHER PUBLICATIONS The Transmission-Line Loudspeaker Enclosure" by A. R. Bailey Wireless World May 1972, Vol. 78, No. 1439 pp. 215-217.

Primary Examiner-Stephen J. Tomsky Attorney, Agent, or Firm-Flynn & Frishauf 57] ABSTRACT Sound reproducing apparatus. for example a loudspeaker unit in a hi-fi system, having a cabinet mounting on its front face a bass speaker unit and having two treble units, one being mounted on each of the front and rear faces of the cabinet.

12 Claims, 11 Drawing Figures U.S. Patent Dec. 2, 1975 II n H n H Sheet 1 of2 Sheet 2 of2 US. Patent Dec. 2, 1975 SOUND REPRODUCING APPARATUS PRIOR APPLICATION Priority, Great Britain November 10th, 1972 application No. 51918/72.

This invention is concerned with sound reproducing apparatus such as loudspeaker systems for use with gramophone, radio and television sets, tape recorders and the like.

The development of amplifiers, pickups and other links in the chain of sound reproduction has reached the point where the inherent distortions are very low but the final result is dependent upon the loudspeaker system and the acoustic environment in which the system is placed, which introduce relatively high and audible levels of distortion of colouration compared with previous links in the chain.

In some domestic living rooms listening conditions may be very far from ideal due to shape, type of furnishing and decoration and the dimensions of the room itself. Listening to music in a room which emphasises strongly certain frequencies, or listening in a small room to sounds beamed directly into the cars can become tiring, as hum, hiss, crackle and other extraneous sounds may be over emphasised. Furthermore, as the range of listening positions in the room may be limited the subjective realisation of the best possible reproduction from the reproducer may fall far short of its potential in ideal conditions.

The introduction of omni-directional sound apparatus whereby reflected sound from walls ceiling and floor of the listening room are used may be less tiring to the ear and create a more spacious effect such that special listening positions are of less importance. Among the criticisms of omni-directional systems, however, is the loss of subjective realism due to the inability to locate a focal point source of the sound, loss of stereophonic information and muddling of the sound.

It is accordingly an object of the present invention to provide a compact sound reproducer with low distortion and which can be used as either a direct frontal radiator or as an omni-directional sound system.

SUMMARY OF THE INVENTION The present invention provides a sound reproducing apparatus comprising a cabinet having front and rear faces, a single low frequency drive unit which is mounted on said front face and a pair of treble units mounted one each on said front and rear faces.

The present invention is also directed to a sound reproducing apparatus comprising a cabinet, a drive unit mounted in the cabinet, the axis of the drive unit being inclined upwardly away from the cabinet, a chamber located in the cabinet at the rear of the drive unit, and a port in the cabinet for the emission of low frequency sound, and a transmission line formed within the cabinet and extending between the chamber and the port.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side elevation of sound reproducing apparatus according to the present invention;

FIG. 2 is a sectional elevation of the apparatus on the line IIII of FIG. 1;

FIGS. 3 and 4 are diagrammatic perspective views of the apparatus of FIGS. 1 and 2, FIG. 4 also showing some modifications of the apparatus;

FIG. 5 illustrates a modified embodiment;

FIGS. 6 and 7 illustrate the operation of the embodiment of FIG. 5;

FIGS. 8, 9 and 10 are respectively front, side sectional and perspective views of a second embodiment; and

FIG. 11 is a partial perspective view of a modification of the embodiment of FIGS. 8-10.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS Referring now to FIGS. 1 to 4 of the drawings, apparatus for reproducing sound includes a cabinet 10 in which are mounted a main drive unit or speaker 11 and treble units 12. The main drive unit 11 is mounted on the front face 10a of the cabinet which defines the front of a chamber 13. The interior of the cabinet is partitioned to define a transmission line which communicates with the chamber 13 and extends to a port 15 in the front of the cabinet. The treble units 12 are mounted one on the front face 10a and one on the rear face 10b of the cabinet 10.

The axis of the main drive unit 11 and of the front facing treble unit 12 is inclined at an angle of 20 to the horizontal and the chamber 13 has an inclined ceiling 16 so that the chamber 13 tapers in cross section from front to rear i.e. away from the unit 11.

The transmission line has four main sections 20a, 20b, 20c and 20d and is defined by the four sidewalls of the cabinet, the base 23 of the chamber 13, and two partitions 21 and 22, the former running from front to rear of the cabinet 10 and the latter extending across the cabinet 10 and being inclined towards the front of the cabinet at its top end. This arrangement of the partitions 21 and 22 ensures that each section of the transmission line tapers i.e. varies in cross section, away from the main drive unit 11.

The first section 20a of the transmission line communicates with the chamber 13 at the rear thereof and extends to the bottom of the cabinet 10 where it communicates transversely with the second section 20b beneath the partition 21. The second section 20b communicates over the top of the transverse partition 22 with the third section 20c and this in turn communicates transverselywith the last section 20d beneath the partition 21. The port 15 is located at the top of the last section 20d of the transmission line.

The vents between the various sections of the transmission line i.e. the spaces beneath the partition 21 and above the partition 22 are varied in size so that no common vent resonance is built up in the transmission line. In this embodiment the vents are made successively smaller along the length of the line towards the port 15. The interior surfaces of the chamber 13 and of the transmission line are lagged with wool and the transmission line is loosely packed with wool filler to absorb and prevent the transmission of unwanted high frequencies.

The total length of the four sections of the transmission line is approximately one quarter of the free space resonant frequency of the cone of the drive unit. This length may be adjusted, however, by means of an adjustable flap 25 at the bottom of the section 200. The flap 25 may be raised to close the vent between the tranmission line sections 20c and 20d and open an alternative port 26 in the bottom of the cabinet 10.

For this reason it is desirable to have the cabinet 10 mounted on legs 30 as illustrated in FIG. 4.

The position of the treble unit 12 in the front of cabinet is not critical and it may be mounted beside the main unit 11, or to the left of the port or above the port 15 which would be lowered a few inches to accomodate the unit 12 (as shown in FIG. 4), the section c of course being blocked off between the port 15 and the treble unit. If the other treble unit is not mounted in the rear wall of the cabinet, the sense of realism is lost. The embodiment described may in fact be modified by dispensing entirely with the treble unit 12 and providing a full range unit instead of the bass main drive unit 11, this of course reducing the stereo information and detail when used in the omni-directional mode due to lack of a focal point source of the sound.

In use the chamber 13 and the transmission line function to absorb and filter out the high frequency output and the resultant reflections from the back of the cone of the main drive unit 11 while allowing the passage of low frequency sound from the port 15 or from the port 26 as desired. Apart from its obvious use with the main drive unit facing the intended audience, the apparatus may also be used with the drive unit facing a wall. The sound reflected from the wall provides a spatial omnidirectional effect and this is intensified by use of alternative port 26. 1

To allow for the two possible modes of operation of the apparatus namely as a direct frontal radiator and as an omni-directional sound system, the angle of inclination of the axis of the main drive unit 11 should preferably be between 10 and 24. This range of angles is also the optimum for the internal acoustics of the chamber 13 and the transmission line. However practical considerations of appearance and ease of manufacture suggest an angle of between 5 and 10.

Additional drive units for mid range and/or treble frequencies may be employed with suitable cross-over networks, and provided that a cross-over frequency above about SOOHz is used they can be mounted in the various positions previously mentioned. In a high quality system, however, it would be desirable to provide separate absorbent filled enclosures behind each unit as is shown in FIG. 1 behind the rear unit 12.

The embodiment described may be further modified by shortening the length of the transmission line to one eighth of the wavelength of the free space resonant frequency of the drive unit cone. This greatly reduces the size of the cabinet with comparatively little sacrifice of quality of sound emission.

A particular modification of the embodiment of FIGS. 1 to 3 is illustrated in FIGS. 5 to 7. A second adjustable flap 50 is provided to open or close the final transmission section 20d to the chamber 13 and simultaneously close or open the front port 15. The flaps and 50 are linked together by a linkage system 51 so that when the flap 25 seals off the section 20d (FIG. 7) the flap 50 opens the section 20d to the chamber 13 via further port 35. In this way the volume of air seen by the main drive unit is the same in either mode while harmonic distortion is reduced.

FIGS. 8 to 10 illustrate a simplified embodiment in which the transmission line has been omitted, this simplified embodiment being particularly useful for small sizes of cabinet. As in the previous embodiments the top of one face to the cabinet in inclined, in this embodiment, at between 10 and 30, to the horizontal. A treble/midrange or treble unit 41 is mounted in the inclined face and beneath it is'positioned a bass or base/- midrange unit 42. Cross bracing 43 is provided for the cabinet and a second treble/midrange or treble unit 45 is provided in the rear face of the cabinet but may be omitted in a book-shelf model to be used flat against a wall but this of course would result in a loss of realism. Also if desired a tuned vent 46 may be provided. This embodiment, while being simpler and enabling the use of a smaller cabinet than the embodiments previously described, still provides satisfactory sound quality when in use in either the direct radiation or omni-directional modes of operation. This last embodiment may be further modified by inclining the other (or rear) face to the horizontal also as shown by cabinet face 40a in FIG. 11. Except for the inclined face 40a, the embodiment of FIG. 11 is identical with the embodiments of FIGS. 810.

By way of clarification it is pointed out that the expression treble unit used herein and in the claims is intended to cover a unit for use at the upper end of the frequency range of the apparatus, e.g. above SOOI-Iz, or indeed a number of such units which together cover the upper end of the frequency range.

I claim:

1. Sound reproducing apparatus comprising:

a cabinet (10) defining at least a first chamber (13) therein, said cabinet (10) having a front face (10a) and a rear face (10b);

a single low frequency drive unit (11) which is mounted in said first chamber (13) on said front face (10a) of said cabinet (10), said chamber (13) extending rearwardly of said low frequency drive unit (1 l at least a treble unit (12), mounted on said front (10a) face of said cabinet (10);

a first port (15) in said cabinet (10) for the emission of low frequency sound;

a four section transmission line (20a, 20b, 20c, 20d) formed within said cabinet (10) and extending between said chamber (13) and said first port (15);

a second port (26) in said cabinet (10) in communication with the third section (20c) of said transmission line; and

an adjustable first flap (25) in said cabinet and selectively movable between first and second positions for respectively opening and closing said second port (26) whereby in said first position said first flap (25) opens said second port (26) to isolate the last section of said transmission line (20d) from the previous transmission line section (200) and in said second position said first flap (25) closes said second port (26).

2. Apparatus as claimed in claim 1, in which means are provided for emitting the sound from at least one of said units on said front face from the apparatus at an angle to the horizontal.

3. Apparatus as claimed in claim 2, in which the axis of at least one of said units on said front face is inclined at an angle to the horizontal of between 5 and 24.

4. Apparatus as claimed in claim 3, in which the axis of the treble unit on the rear face is inclined at an angle to the horizontal.

5. Apparatus as claimed in claim 3 in which said angle is between 5 and 24.

6. Apparatus as claimed in claim 5, in which said angle is between 5 and l0.

7. Apparatus as claimed in claim 1', including:

a further port (35) providing direct access from said chamber (13) to said last section (20d) of said transmission line; and

10. Apparatus as claimed in claim 1, in which said second port (26) is in the bottom of said cabinet (10), and said first port (15) is in the front face (10a) of said cabinet (10).

11. Apparatus as claimed in claim 7, in which said second port (26) is in the bottom of said cabinet (10), and said first port (15) is in the front face (10a) of said cabinet (l0).

12. Apparatus as claimed in claim 1, which includes a further treble unit (12) mounted on said rear (10b) face of said cabinet (10). 

1. Sound reproducing apparatus comprising: a cabinet (10) defining at least a first chamber (13) therein, said cabinet (10) having a front face (10a) and a rear face (10b); a single low frequency drive unit (11) which is mounted in said first chamber (13) on said front face (10a) of said cabinet (10), said chamber (13) extending rearwardly of said low frequency drive unit (11); at least a treble unit (12), mounted on said front (10a) face of said cabinet (10); a first port (15) in said cabinet (10) for the emission of low frequency sound; a four section transmission line (20a, 20b, 20c, 20d) formed within said cabinet (10) and extending between said chamber (13) and said first port (15); a second port (26) in said cabinet (10) in communication with the third section (20c) of said transmission line; and an adjustable first flap (25) in said cabinet and selectively movable between first and second positions for respectively opening and closing said second port (26) whereby in said first position said first flap (25) opens said second port (26) to isolate the last section of said transmission line (20d) from the previous transmission line section (20c) and in said second position said first flap (25) closes said second port (26).
 2. Apparatus as claimed in claim 1, in which means are provided for emitting the sound from at least one of said units on said front face from the apparatus at an angle to the horizontal.
 3. Apparatus as claimed in claim 2, in which the axis of at least one of said units on said front face is inclined at an angle to the horizontal of between 5* and 24*.
 4. Apparatus as claimed in claim 3, in which the axis of the treble unit on the rear face is inclined at an angle to the horizontal.
 5. Apparatus as claimed in claim 3 in which said angle is between 5* and 24*.
 6. Apparatus as claimed in claim 5, in which said angle is between 5* and 10*.
 7. Apparatus as claimed in claim 1, including: a further port (35) providing direct access from said chamber (13) to said last section (20d) of said transmission line; and a further flap (50) operable between a first position to seal said first port (15) and open said further port (35), and a second position to seal said further port (35) and open said first port (15).
 8. Apparatus as claimed in claim 7, including means (51) interconnecting said first flap (25) and said further flap (50) for simultaneous operation to said first or second positions.
 9. Apparatus as claimed in claim 1, in which said first port is in communication with the fourth section (20d) of said transmission line.
 10. Apparatus as claimed in claim 1, in which said second port (26) is in the bottom of said cabinet (10), and said first port (15) is in the front face (10a) of said cabinet (10).
 11. Apparatus as claimed in claim 7, in which said second port (26) is in the bottom of said cabinet (10), and said first port (15) is in the front face (10a) of said cabinet (10).
 12. Apparatus as claimed in claim 1, which includes a further treble unit (12) mounted on said rear (10b) face of said cabinet (10). 